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Removal of selenate (SeO42-) from selenate-contaminated wastewater is challenging due to the commonly coexisting and competing anions of sulfate (SO42-) and nitrate (NO3-). This study investigates SeO42- reduction to elemental selenium (Se0) in a cathode-based bioelectrochemical (BEC) reactor and a conventional biofilm reactor (i.e., an upflow anaerobic reactor). The simulated wastewater contained SeO42- at a typical concentration of 5 mg Se/L, SO42- at a typical concentration of 1000 mg S/L, and NO3- at concentrations that varied from 0 to 10 mg N/L. The impact of sulfate on the BEC reactor was much lower than that on the conventional reactor: The selenium removal, defined as (selenate in influent – dissolved selenium in effluent)/selenate in influent, was 99 % in the BEC reactor versus 69 % in the conventional biofilm reactor. The lower selenium removal in the conventional reactor was mainly due to the >10 times higher reduction of sulfate, which directly caused competition between sulfate and selenate for the common resources such as electrons. The more reduction of sulfate in the conventional reactor further led to 45 times higher production of selenide. Selenide is usually assumed to be minimal and therefore not measured in the literature. This simplification may significantly overestimate selenium removal when the influent sulfate concentration is very high. NO3- in the influent of the BEC reactor promoted selenium removal when it was less than 5.0 mg N/L but inhibited selenate removal when it was more than 7.5 mg N/L. This was supported by the microbial community analysis and intermediate (nitrite) analysis. 

Tellurium is a critical mineral for the foreseeable future due to its scarcity and importance in future energy technology. A biocathode of a bioelectrochemical reactor (BEC) was used for the first time to extracellularly reduce TeO32- in simulated wastewater to elemental Te0 nanorods, which could potentially be recovered. Scanning transmission electron microscopy revealed that only 2% of the cells on the biocathode contained intracellular Te0 nanorods. In contrast, in the conventional bioreactor (CBR), 40% of the cells contained intracellular Te0 nanorods. Raman spectroscopy determined that the Te0 nanorods were trigonal and amorphous Te0. Microbial community analysis showed the dominance of Pseudomonas, Stenotrophomonas, and Azospira phylotypes in the cathode chamber, despite being < 8% in the inoculum. They were all putative TeO32- reducers due to their known ability to reduce tellurite and transfer extracellular electrons. The TeO32- removal efficiency in the BEC reactor reached 97% when the influent TeO32- was 5 mg Te/L. The reactor operating conditions, including the flow rate, the external resistor, and the cation exchange membrane, were optimized. This work demonstrates the potential of BEC reactors for continuous and green synthesis of Te0 nanorods. 

Abstract The ocean microbe‐metabolite network involves thousands of individual metabolites that encompass a breadth of chemical diversity and biological functions. These microbial metabolites mediate biogeochemical cycles, facilitate ecological relationships, and impact ecosystem health. While analytical advancements have begun to illuminate such roles, a challenge in navigating the deluge of marine metabolomics information is to identify a subset of metabolites that have the greatest ecosystem impact. Here, we present an ecological framework to distill knowledge of fundamental metabolites that underpin marine ecosystems. We borrow terms from macroecology that describe important species, namely “dominant,” “keystone,” and “indicator” species, and apply these designations to metabolites within the ocean microbial metabolome. These selected metabolites may shape marine community structure, function, and health and provide focal points for enhanced study of microbe‐metabolite networks. Applying ecological concepts to marine metabolites provides a path to leverage metabolomics data to better describe and predict marine microbial ecosystems. 

Microbial processes are crucial in the redox transformations of toxic selenium oxyanions. This study focused on isolating an efficient selenate-reducing strain, Azospira sp. A9D-23B, and evaluating its capability to recover extracellular selenium nanoparticles (SeNPs) from selenium-laden wastewater in different reactor setups. Analysis using transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX) revealed significantly higher extracellular SeNPs production (99%) on the biocathode of the bioelectrochemical (BEC) reactor compared to the conventional bioreactor (65%). Further investigations into the selenate reductase activity of strain A9D-23B revealed distinct mechanisms of selenate reduction in BEC and conventional bioreactor settings. Notably, selenate reductases associated with the outer membrane and periplasm displayed higher activity (18.31 ± 3.8 µmol/mg-min) on the BEC reactor's biocathode compared to the upflow anaerobic conventional bioreactor (3.24 ± 2.9 µmol/mg-min). Conversely, the selenate reductases associated with the inner membrane and cytoplasm exhibited lower activity (5.82 ± 2.2 µmol/mg-min) on the BEC reactor's biocathode compared to the conventional bioreactor (9.18 ± 1.6 µmol/mg-min). However, the comparable kinetic parameter (K_m) across cellular fractions in both reactors suggest that SeNPs localization was influenced by enzyme activity rather than selenate affinity. Overall, the mechanism involved in selenate reduction to SeNPs and the strain's efficiency in detoxifying selenate below levels regulated by U.S. Environmental Protection Agency have broad implications for sustainable environmental remediation strategies. 

Abstract With the dramatic decrease in fossil fuel stocks and their detrimental effects on the environment, renewable energy sources have gained imminent importance in the mitigation of emissions. As lipid-enriched energy stocks, cyanobacteria are the leading group of microorganisms contributing to the advent of a new energy era. In the present study, the impact of Nanofer 25 s nanoscale zero-valent iron nanoparticles (nZVIs) and ampicillin on lipid production and cellular structural changes inFremyella diplosiphonstrain B481-SD were investigated. Total lipid abundance, fatty acid methyl ester (FAME) compositions, and alkene production as detected by high-resolution two-dimensional gas chromatography with time-of-flight mass spectrometry (GC × GC/TOF–MS) was significantly higher (p < 0.05) in the individual application of 0.8 mg/L ampicillin, 3.2 mg/L nZVIs, and a combined regimen of 0.8 mg/L ampicillin and 3.2 mg/L nZVIs compared to the untreated control. In addition, we identified significant increases (p < 0.05) in monounsaturated fatty acids (MUFAs) inF. diplosiphontreated with the combination regimen compared to the untreated control, 0.8 mg/L of ampicillin, and 3.2 mg/L of nZVIs. Furthermore, individual treatment with 0.8 mg/L ampicillin and the combination regimen (0.8 mg/L ampicillin + 3.2 mg/L nZVIs) significantly increased (p < 0.05) Nile red fluorescence compared to the untreated control, indicating neutral membrane lipids to be the main target of ampicillin added treatments. Transmission electron microscopy studies revealed the presence of single-layered thylakoid membranes in the untreated control, while complex stacked membranes of 5–8 layers were visualized in ampicillin and nZVI-treatedF. diplosiphon. Our results indicate that nZVIs in combination with ampicillin significantly enhanced total lipids, essential FAMEs, and alkenes inF. diplosiphon. These findings offer a promising approach to augment the potential of using the strain as a large-scale biofuel agent.